MERCURY

Mercury is the planet closest to the Sun, and experiences
scorching temperatures by day. But it has virtually no atmosphere to trap the
heat, so is freezing at night. It is a rocky planet, just over a third the
diameter of Earth. Its surface is covered with craters, which make it look
similar to parts of the Moon. These craters were formed when the planet was
bombarded with meteorites long ago.

Table 9. ESSENTIAL DATA

Diameter at equator

4,880 km (3,032 miles)

Average distance from Sun

57.9 million km (36 million miles)

Orbital period

88 days

Rotation period

58.7 days

Mass (Earth=1)

0.06

Gravity (Earth=1)

0.38

Average surface temperature

167°C (332°F)

Number of moons

0

The craters that cover almost all of the surface of Mercury are
generally shallower than those on the Moon. They vary in size from a few metres
to hundreds of kilometres across. In between, there are relatively smooth
lava-covered plains crossed by cliffs and ridges.